The present invention relates to steam generators.
In particular, the present invention relates to a steam generator having a bundle of U-shaped tubes and a signal tube plate, with the fluid which is to be converted into steam engaging the exterior of the tubes while the medium from which heat is extracted flows along the interior of the tubes.
Conventional steam generators of this general type are capable of generating a wet steam which is dried by utilizing special coarse and fine separating units. Such constructions have drawbacks in that they produce only saturated steam or dry saturated steam, so that only a relatively low thermal efficiency can be achieved. Because of the water separating devices such steam generators are relatively large so that because of the large volume required for such installations, the housing in which they are contained, particularly in the case of nuclear steam generators, are undesirably large. Furthermore, it is conventional to support such upright steam generators at their lower ends. The conduits for the live steam are situated, however, at the opposite upper ends of the steam generators. As a result such conduits for the live steam must be capable of elastically absorbing the entire expansion and contraction of the steam generator and thus have an undesirably great length.
A further drawback of such steam generators results from the manner in which the fluids are circulated. During operation of such steam generators the circulating water becomes rich in impurities with the latter achieving undesirably high concentrations which ultimately bring about corrosion at expansion cracks and intercrystalline corrosion at the location where the austenitic or high-alloy tubes of the steam generator are joined with the tube plate. These corrosion effects are favored by the pronounced deformation of the tubes which is required in connection with the rolling of the ends of the tubes during connection of the latter with the tube plate.